A Catechol/AES/LTS Ternary Formulation for Permeability-Dependent Oil Mobilization and Fluid Redistribution in Low-Permeability Sandstone

Abstract Low-permeability sandstone reservoirs under high-temperature/high-salinity conditions present coupled challenges of capillary trapping, restricted injectivity, surfactant instability, and heterogeneous sweep. In this study, a catechol/AES/LTS ternary formulation was developed to combine hard-brine compatibility with strong interfacial oil mobilization. LTS acted as the principal interfacially active component, AES improved dispersion stability in Ca2+-rich brine, and catechol served as an aging-responsive auxiliary component capable of interacting with divalent ions. The best-performing formulation among those tested, containing 0.05 wt % catechol, 0.05 wt % AES, and 0.20 wt % LTS, reduced the oil-water interfacial tension to approximately 0.004 mN/m and produced the strongest microfluidic oil-removal and current-response behavior among the tested formulations. During 15 days of aging at 70 °C, the catechol-containing formulation underwent oxidation-associated self-acidification to approximately pH 4.6 while retaining smaller apparent hydrodynamic aggregates, less macroscopic precipitation, and lower aged IFT than the catechol-free AES/LTS control. Rock-contact fluorescence and CLSM measurements further showed treatment-induced redistribution of fluorescent/optically active surface-associated material, although these optical measurements were not chemically specific for either residual-oil or catechol-derived products. Comparative core flooding and LF-NMR showed formulation-dependent fluid redistribution at two permeability levels. In the approximately 26 mD sandstone, the catechol-containing core exhibited greater oil recovery and increased aqueous occupancy of restricted relaxation domains, with local preferential-path restriction remaining a possible contributing process. In the approximately 0.4 mD sandstone, the larger within-core reduction in oil-associated NMR signal was accompanied by increased aqueous signal across both restricted and movable domains. These results support an integrated chemical-flooding strategy coupling hard-brine compatibility, IFT-enabled oil mobilization, and permeability-dependent fluid redistribution. Permanent plugging and mineral-scale acid etching are not independently established by the present measurements.